The invention relates to a device for supplying boiling water.
The prior art in the field of hot water supplying devices is fairly extensive. The prior art comprises, on the one hand, the devices which dispense hot water and, on the other, the devices which are designed for supplying boiling water.
The first group of devices includes the well known household boilers, which are so constructed that the water present therein can never reach the temperature of the atmospheric boiling point, Which is accomplished in particular by means of a thermostat ensuring that a water temperature of, for instance, 85.degree. C., is not exceeded, and in any case, that the boiling temperature of the water is not reached. The water in these boilers is present therein under normal water mains pressure and the boiler, as well as the water outlet conduits connected thereto, are completely filled with water, so that the outflow of the water, too, occurs under water mains pressure and upon withdrawal of water invariably an initial flow of water is obtained whose temperature is lower than that of the water in the boiler. The pressure increase to be expected during the heating of the water in the boiler to a temperature close to its boiling point, the relatively large quantity of water present in household boilers, as well as the substantial scale formation to be expected at temperatures close to the boiling point, are reasons why achieving temperatures in the neighbourhood of the boiling point of water under atmospheric pressure is carefully avoided in devices as described hereinabove.
For many domestic purposes, for instance for making small quantities of coffee or tea, or for preparing small quantities of food, but also in laboratories, etc., it is desirable that small quantities of boiling water can be made available directly. It is noted here that there are important physical differences between boiling water on the one hand and heated, but not boiling, water, on the other, inter alia because boiling or thoroughly boiled water contains practically no carbon dioxide.
There are known so-called through-flow devices, which operate without pressure, i.e. the pressure on the water to be heated is the atmospheric pressure and the water is not heated to the temperature of the atmospheric boiling point until water is drawn off.
Known also are boiling-water devices, in which the water is maintained at a superatmospheric temperature in a reservoir and in which a thermostat is set at a value which is above the boiling point of water under atmospheric pressure. In these known boiling-water devices, the proposed, often complicated, construction was dictated by the fear that the pressure in the device would rise too high or that the cold and hot water would mix. The development of the prior art concerned is described in a series of four patent specifications.
Thus, GB patent specification 706,866 discloses a boiling-water device of the type described hereinabove, in which a limited water inlet is provided for, so as to allow the cold incoming water to be heated to the desired temperature before it comes into contact with the rest of the water. In this type of device, the incoming amount of cold water is kept so small that it can be heated to the reservoir temperature while it flows along the heating element and then leaves the reservoir through the outlet arranged adjacent the bottom. The hot water supply in the reservoir is drawn upon as soon as per unit time more water is being withdrawn than is flowing in through the limited inlet. In that case the outflow pressure is determined by the vapour pressure of the water in the boiler and this is relatively low and not constant. To make maximum use of the reservoir contents, it is required that the outlet conduit is connected at the lowest possible point in the reservoir. Further, in devices of this type the water inlet must be limited severely, in view of the high specific heat of water and the relatively large amount of energy which is required for heating a given quantity of water to above its boiling point under atmospheric pressure.
In U.S. Pat. No. 2,786,126 the development as described in GB patent specification 706,866 is carried on, but now a particular control valve is used in the inlet circuit, so the incoming water cannot cool the water stored below the desired temperature. It is striking, but understandable in view of the object contemplated, that both the water inlet and the water outlet terminate in the direct vicinity of the heating element.
U.S. Pat. No. 2,852,656 discloses a device in which there is no limited water inlet and in which means for drawing off boiling water are connected to the top part of the reservoir, i.e. not in the direct vicinity of the heating element. However, it appears from the disclosure in that patent specification, that again all precautions have been taken to pass the incoming water directly along the heating element, so as to adjust it to the temperature of the water already present in the reservoir as fast as possible, so as to prevent cooling of the water already present by the incoming water.
Finally, in U.S. Pat. No. 2,894,109 again mention is made of the fear that incoming cold water will cool the water present in the reservoir, but this time again recourse is taken to the use of a limited water inlet circuit, accomplished by means of a specially designed control valve, while the water inlet and the water outlet are again so arranged that they terminate in the direct vicinity of the heating element.
The devices described hereinabove have never gained practical application, presumably owing to their complicated construction and the associated problems encountered during use.
The invention as described in Netherlands patent specification 172,589 was based on the finding that the problem of incoming water cooling the reservoir contents does not arise in practice, and that without particular steps being taken, a good separation of cold and hot water remains present.
The device as described in that patent specification is of the type as described in U.S. Pat. No. 2,852,656. It comprises a thermally insulated compression resistant water reservoir, an electric heating element of such power that the water present in the reservoir is heated to above its atmospheric boiling point, a temperature control with which the temperature of the water in the reservoir is set above its boiling temperature under atmospheric pressure, a water inlet circuit, which is connected to the water mains and which is suitable for supplying an inlet flow which is at least equal to the delivery flow of the device, as well as means for drawing off boiling water joined directly to the reservoir and connected to the top part thereof.
In that device the water inlet circuit terminates under or at the underside of the heating element, while, preferably, there is arranged in the reservoir adjacent the water inlet a water divider for the incoming water to prevent the mixing of incoming cold water and the hot water present.
As described in that patent specification, in that device the cold/hot separation is maintained so well that more than 80% of the water contents can be withdrawn from the reservoir without the temperature thereof falling below the boiling temperature under atmospheric pressure. In the patent specification it is observed that this is surprising, the more so because the device described is intended for domestic use in particular, and accordingly is relatively small, having particularly a volume of less than 10 liters, more particularly of approximately 5 liters, so that precisely in such a device a high degree of mixing could be expected.
Although the device as described in Netherlands patent specification 172,589 has proved its merits in practice, its use is accompanied by a number of as yet unsolved problems, so that it has not become generally used.
One of these problems is that the discharge conduit for the boiling water must be kept as short as possible, so as to limit an initial flow of cold, at least not boiling, water as much as possible. In practice, this causes problems, because then the discharge orifice is not disposed sufficiently high above a working surface, for instance a sink or the like, leaving too little space to place a mug, a pot or the like, under the discharge orifice. Moreover, the necessity of a short discharge conduit requires that the device be arranged directly under the sink top or the like. In practice, this is not always possible.
In the known device, the discharge valve is arranged at the end of the discharge conduit, so as to prevent the egressing water drops in the discharge conduit from being accelerated too strongly by the expanding, 20-fold volume amount of steam. Moreover, as described, this discharge valve must be of a particular construction to prevent the water spurting from the outlet orifice like a spray.
In practice, this position of the discharge valve leads to two important disadvantages. Because the entire device. i.e. up to the discharge valve, is filled with water, the use of this device inevitably involves some initial flow of cold water. In view of the fact that the device is used for supplying small quantities of boiling water, for instance for making a single cup of tea or coffeee, any initial flow of cold water is altogether unacceptable to the user. Moreover, the tap arranged at the end of the discharge conduit will inevitably exhibit a measure of dripping.
It is an object of the present invention to provide a solution to the problems outlined hereinabove.